New study explains surprising acceleration of Greenland's inland ice

Jul 17, 2013

Meltwater from the surface of the Sermeq Avannarleq Glacier drains down toward interior ice. This photograph depicts a region about 10 miles from the ice sheet margin in Southwest Greenland. A new CIRES-led study helps explain the surprising acceleration of inland ice. Meltwater draining through the ice likely warms the ice sheet from the inside and like a stick of warm butter, the sheet softens, deforms and can flow faster. Credit: William Colgan/CIRES

Surface meltwater draining through cracks in an ice sheet can warm the sheet from the inside, softening the ice and letting it flow faster, according to a new study by scientists at the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado Boulder.

During the last decade, researchers have captured compelling evidence of accelerating ice flow at terminal regions, or "snouts," of Greenland glaciers as they flow into the ocean along the western coast. The new CIRES research now shows that the interior regions also are flowing much faster than they were in the winter of 2000-01, and the paper proposes a reason for the speedup.

"Through satellite observations, we determined that an inland region of the Sermeq Avannarleq Glacier, 40 to 60 miles from the coast, is flowing about one and a half times faster than it was about a decade ago," said Thomas Phillips, lead author of the new paper and a CIRES research associate at the time of the study. In 2000-01, the inland segment was flowing at about 130 feet (40 meters) per year; in 2007-08, that speed was closer to 200 feet per year (60 meters).

"At first, we couldn't explain this rapid interior acceleration," Phillips said. "We knew it wasn't related to what was going on at the glacier's terminus. The speedup had to be due to changes within the ice itself."

To shed light on the observed acceleration, Phillips and his team developed a new model to investigate the effects of meltwater on the ice sheet's physical properties. The team found that meltwater warms the ice sheet, which then—like a warm stick of butter—softens, deforms and flows faster.

Previous studies estimated that it would take centuries to millennia for new climates to increase the temperature deep within ice sheets. But when the influence of meltwater is considered, warming can occur within decades and produce rapid accelerations. The paper has been accepted for publication in the Journal of Geophysical Research: Earth Surface, a journal of the American Geophysical Union.

The CIRES researchers were tipped off to this mechanism by the massive amount of meltwater they observed on the ice sheet's surface during their summer field campaigns, and they wondered if it was affecting the ice sheet. During the last several decades, atmospheric warming above the Greenland Ice Sheet has caused an expanding area of the surface to melt during the summer, creating pools of water that gush down cracks in the ice. The meltwater eventually funnels to the interior and bed of the ice sheet.

As the meltwater drains through the ice, it carries with it heat from the sun.

"The sun melts ice into water at the surface, and that water then flows into the ice sheet carrying a tremendous amount of latent energy," said William Colgan, a co-author and CIRES adjunct research associate. "The latent energy then heats the ice."

The new model shows that this speeds up ice flow in two major ways: One, the retained meltwater warms the bed of the ice sheet and preconditions it to accommodate a base layer of water, making it easier for the ice sheet to slide by lubrication. Two, warmer ice is also softer (less viscous), which makes it flow more readily.

"Basically, the gravitational force driving the ice sheet flow hasn't changed over time, but with the ice sheet becoming warmer and softer, that same gravitational force now makes the ice flow faster," Colgan said.

This transformation from stiff to soft requires only a little bit of extra heat from meltwater. "The model shows that a slight warming of the ice near the ice sheet bed—only a couple of degrees Celsius—is sufficient to explain the widespread acceleration," Colgan said.

The findings have important ramifications for ice sheets and glaciers everywhere. "It could imply that ice sheets can discharge ice into the ocean far more rapidly than currently estimated," Phillips said. "It also means that the glaciers are not finished accelerating and may continue to accelerate for a while. As the area experiencing melt expands inland, the acceleration may be observed farther inland."

The new model will help scientists more accurately forecast these impacts, and it is being incorporated into Earth-system models for predicting future ice discharge from the Greenland Ice Sheet.

The findings suggest that to understand future sea-level rise, scientists need to account for a previously overlooked factor—meltwater's latent energy—and its potential role in making glaciers and ice sheets flow faster into the world's oceans. In 2007, the Intergovernmental Panel on Climate Change (IPCC) wrote that one of the most significant challenges in predicting sea-level rise was "limited" understanding of the processes controlling ice flow. This paper, and others that have advanced scientific understanding of ice sheet and glacier behavior, are likely to inform the IPCC's next assessment, due out in 2014.

"Traditionally, latent energy has been considered a relatively unimportant factor, but most glaciers are now receiving far more meltwater than they used to and are increasing in temperature faster than previously imagined," Colgan said. "The chunk of butter known as the Greenland Ice Sheet may be softening a lot faster than we previously thought possible."

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User comments : 15

I can handle the creationists since they are countered by courts when they merely threaten to drop a few paragraphs into state school textbooks, and their stem cell research funding ban is finally becoming moot, but Global Warming really is a full force encroachment of religion into the state. That it's Scientology worthy computer model doomsday prophesy refuses to show up means it has already reached its expiration date. Alas, when the backlash reaches full force it will re-enable the old school attacks on science, as human folly ever increases.

Greenland and especially Antarctica exist far below the freezing point of water except perhaps for a few days a year, so natural warming that increases humidity and snowfall causes it to grow just as mild natural warming indeed causes floating arctic ice to melt a bit.

Greenland snow cover has been boringly *increasing* for decades as research stations suffer being buried:

Sea level data from satillites shows utterly no trend change as CO2 output from China and India has boomed, strongly countering claims that Greenland melting along its edges is having any effect above the natural trend:

The hoax nature of Climatology is revealed in how it has become standard PR procedure to cut utterly linear 150 year old tide gauge data off in the satellite era to imply that the systematic mismatch between tide gauge (relative to shore) and satillite data (absolute) represents a sudden jump in real world sea level trend, such behavior being the very definition of junk science!

This very article has its fancy photograph featured on NASA's climate site today, offering a natural chance to once again ask, hey...why is the tide gauge "GROUND DATA" data cut off on the sea level entry on their site so to delete the last last two *decades* of tide gauge data that overlaps the satillite era?:

...also, why does their climate page, meant to inform policy makers and the public alike only show a graph of arctic ice extent instead of the gradually cooling Antarctic that represents a whopping 90% of ice on the planet?

See for yourself why that might be and ask yourself what might be the effect on sea level when the vast majority of planetary ice mass shows the following trend that will naturally swamp Arctic ice effects by a whopping 9X factor:

(1) Why did they call it Greenland and did it slip into the ocean during its farming era or when ice core data say it was much hotter for thousands of years until the Vikings settled there?(2) Why has Greenland sea ice extent shown utterly no loss in our high CO2 millennium?:

... why does their climate page, [snip] only show a graph of arctic ice extent instead of the gradually cooling Antarctic that represents a whopping 90% of ice on the planet?..........[snip] effect on sea level when the vast majority of planetary ice mass shows the following trend that will naturally swamp Arctic ice effects by a whopping 9X factor:

Because Antarctica is a very different place:A land-mass with ave height 12000ftIsolated from other land masses and insulated from ocean warming via the ACC.Further isolated by CFC influenced cooling of the winter Stratospheric vortex.Sea Ice is very different from land-ice.Arctic ice is 2x as thick.Do I take it you are implying that the Antarctic sea-ice trend upward is countering the Arctic sea-ice loss?

"While thickness varies significantly within both regions, Antarctic ice is typically 1 to 2 meters (3 to 6 feet) thick, while most of the Arctic is covered by sea ice 2 to 3 meters (6 to 9 feet) thick. Some Arctic regions are covered with ice that is 4 to 5 meters (12 to 15 feet) thick."

Sea ice is a thin sliver along the coast and some slush covering the North Pole, but the fact that Antarctic sea ice area is growing supports the obvious source of that growth as being the growth of the bulk of 90% of world ice on a steadily cooling continent which remains about a hundred degrees below the point where Global Warming might cause bulk melting. I had indeed oversimplified this argument into an imprecise soundbite.

Sea ice is a thin sliver along the coast and some slush covering the North Pole, but the fact that Antarctic sea ice area is growing supports the obvious source of that growth as being the growth of the bulk of 90% of world ice on a steadily cooling continent which remains about a hundred degrees below the point where Global Warming might cause bulk melting. I had indeed oversimplified this argument into an imprecise soundbite.

No my post shows that the energy locked away as LH is being released by the imbalance in meltvsgrowth between the two poles. By a ratio of 10:1.

Update: NASA's ICESat satellite provided real data on both Greenland and Antarctic ice mass by simple laser altimetry and some simple ice density theory minus any convoluted statistics, between 2003 and 2008. It showed that the edges of Greenland are melting but the interior is not and that exactly half (100 gigatons/year vs. 49 gigatons/year) of Greenland melt mass was offset by *gains* in Antarctic ice mass. My 9X claim above was incorrect in the current day and I can only offer another hand waving argument that 90% of planetary ice mass will become more instead of less of a sea level sink if natural warming continues, enhanced by a bit of CO2 forcing. The claim is based on even more basic physics than greenhouse theory, namely that a huge uber cold ice mass will grab lots of snow in a more humid world.

Thankyou for your honest admission.The misperception lies with the equating of "ice/snow" and "temperature".The Arctic environment is so extreme ( even if from height alone ) that it will build up extra snow/ice for many centuries yet. It would though lose ice at the periphery. As SST's rise then snowfall will increase ( due ability of warmer air to hold more moisture ). While ever the Temp of the cloud is near 0C at least it will snow. Snowfall at freezing point can be twice that that -10C yields.The idea that the behaviour of ice in Antarctica contradicts general warming, is just that, a misperception.